## Breadcrumb - [Home](/) - [Living with Parkinson's](/living-with-parkinsons) - [Treatment](/living-with-parkinsons/treatment) - [Prescription Medications](/living-with-parkinsons/treatment/prescription-medications) ## Breadcrumb - [Home](/) - [Living with Parkinson's](/living-with-parkinsons) - [Treatment](/living-with-parkinsons/treatment) - [Prescription Medications](/living-with-parkinsons/treatment/prescription-medications) # COMT Inhibitors ## 💡 Quick Summary - COMT inhibitors extend the effect of [levodopa](/living-with-parkinsons/treatment/prescription-medications/levodopa "Levodopa") to reduce “wearing off” and increase “on” time. - These medications are taken only with levodopa and include entacapone, tolcapone, Stalevo and opicapone. - Common side effects include diarrhea, discolored urine, [dyskinesia](/understanding-parkinsons/movement-symptoms/dyskinesia "Dyskinesia") and confusion. - Medication interactions should be reviewed with a doctor or pharmacist. ![Closeup shot of pharmacists putting medicine in a bag](/sites/default/files/styles/no_sizing/public/images/comtinhibitors.jpg?itok=azPyrs3N) This class of Parkinson’s disease (PD) medications has little to no direct effect on symptoms but is used to prolong the effect of the Parkinson’s medication [levodopa](/living-with-parkinsons/treatment/prescription-medications/levodopa "Levodopa") by blocking its break down. Catechol-O-methyl transferase (COMT) inhibitors are used primarily to help with “[wearing off](/library/fact-sheets/managing-off-time "Managing "Off" Time in Parkinson's")” *—* changes in the ability to move as the effect of levodopa becomes short-lived. ## Quick Facts - Catechol-O-methyl transferase (COMT) is a body enzyme. When a person takes levodopa, COMT can deactivate levodopa before it enters the brain and central nervous system; COMT inhibitors prevent this from happening. - COMT inhibitors are most effective when used in combination with levodopa to extend “on” time. ## Forms of COMT Inhibitors - ### Entacapone (Comtan®) **Available Doses:** 200 mg **Typical Treatment Regimen**: 4 to 8 times per day (with each levodopa dose) **Side Effects**: Diarrhea, discolored urine, enhanced side effects of levodopa (especially dyskinesia and confusion) **Indications for Usage**: Combination therapy with levodopa for motor fluctuations, not used without levodopa. - ### Tolcapone (Tasmar®) **Available Doses:** 100 mg, 200 mg **Typical Treatment Regimen**: 100 mg up to 3 times per day, to a maximum of 200 mg 3 times per day **Side Effects**: Diarrhea, discolored urine, enhanced side effects of levodopa (especially [dyskinesia](/understanding-parkinsons/movement-symptoms/dyskinesia "Dyskinesia") *—* involuntary muscle movements in response to levodopa *—*and confusion), risk of liver damage (need regular blood tests to check liver functions) **Indications for Usage**: Combination therapy with levodopa for motor fluctuations, not used without levodopa. Should only be used after all PD medications have been tried and should be discontinued if no benefit in 3 weeks. Due to instances of liver function abnormalities during clinical trials of tolcapone, the Food and Drug Administration mandates that blood tests of liver function be conducted at the beginning of the treatment and every six months after beginning treatment - ### Carbidopa-levodopa-entacapone Tablets (Stalevo) *This is a combination drug which includes entacapone and carbidopa-levodopa in one pill. It is more convenient compared with carbidopa-levodopa and entacapone taken separately.* **Available Doses:** 12.5-50-200 mg, 18.75-75-200 mg, 25-100-200 mg, 31.25-125-200 mg, 37.5-150-200 mg, 50-200-200 mg **Typical Treatment Regimen**: 150 to 1,600 mg of levodopa total daily dose, depending on daily need (maximum 8 tablets daily) **Common Side Effects**: nausea, lower blood pressure, confusion, dyskinesia (extra movements), diarrhea and discolored urine **Indications for Usage**: Replacement for carbidopa-levodopa for motor fluctuations, with the benefit of entacapone, which extends the life of levodopa - ### Opicapone (Ongentys®) **Available Doses**: 25 mg, 50 mg capsules **Typical Treatment Regimen**: 50 mg by mouth once daily at bedtime **Side Effects**: dyskinesia, constipation, low blood pressure/dizziness, weight loss **Indications for Usage**: Combination therapy with levodopa for "off" time (not pharmacologically active by itself). ## Common Side Effects of COMT Inhibitors - May exaggerate some levodopa-related side effects, especially dyskinesia - Confusion - Hallucinations - Discoloration of urine (reddish brown or rust-colored) - Diarrhea - ### Disclaimers Please note that the side effects listed in the tables that accompany each class of medication are the most *commonly experienced*. Not all individuals will experience such side effects. Careful adjustments to dosage or the timing of individual doses can often effectively limit or eliminate side effects for many people. Speak to your doctor immediately if you experience any side effects. For a complete description of each drug and its possible side effects, please request a “package insert” from your pharmacist for each drug used. **It is recommended that all prescriptions be filled at the same pharmacy to avoid interactions between medications.** Interactions can be dangerous and even life-threatening, so make sure the pharmacist knows of all medications and supplements being taken, including over-the-counter medications and supplements. **Caution:** Parkinson’s medications may have interactions with certain foods, other medications, vitamins, herbal supplements, over-the-counter cold pills and other remedies. Anyone taking a PD medication should talk to their doctor and pharmacist about potential drug interactions. *Page reviewed by Dr. Chauncey Spears, Clinical Assistant Professor and Dr. Amelia Heston, Movement Disorders Fellow at the University of Michigan.* ## Related Materials Podcasts ### [ Episode 96: PD Medications and Side Effects ](/library/podcast/96) [Listen Now](/library/podcast/96) Books ### [ Medications: A Treatment Guide to Parkinson’s Disease ](/library/books/medications) [Read Now](/library/books/medications) Podcasts ### [ Episode 109: Medication Timing ](/library/podcast/109) [Listen Now](/library/podcast/109) ## Related Blog Posts ![Couple buying medication in a store](/sites/default/files/styles/500x360/public/images/pdmednew-bloghero.png?h=ed9ce7df&itok=xE6j_DbB) Raise Awareness ### [ PD and Medication: What's New? ](/blog/tips/2019-medication-update) READ NOW ![Couple looking at papers](/sites/default/files/styles/500x360/public/images/medicationtherapy-blog.jpg?h=ed9ce7df&itok=4L9hOKes) Advancing Research ### [ What's Hot in PD? When should you start medication therapy for Parkinson’s disease? ](/blog/research/starting-medications) READ NOW ![Woman giving man pill](/sites/default/files/styles/500x360/public/images/latestpdmedications-personalizedapproach-blog.jpg?h=ed35b813&itok=I8N-GybY) Raise Awareness ### [ The Latest in Parkinson’s Medications: Taking a Personalized Approach ](/blog/awareness/personalized-medications) READ NOW ### Order a Parkinson’s Hospital Safety Guide The Hospital Safety Guide is a resource for people with Parkinson's and their care partners filled with useful tools and information to prepare for and navigate a hospital stay. [ORDER NOW](/resources-support/pd-library/order-publications) [LEARN MORE](/resources-support/hospital-safety-guide) - Share on Facebook - Share on X - Share on LinkedIn